In the case of geologically disturbed, methane-containing coal deposits which have small dimensions and which are of high strength, mechanical mining has not yet been perfected. In coal mines working under these conditions, the applied method, apart from manual loosening, is mainly by short hole loosening and/or breaking by a single breaking cylinder, functioning with high pressure compressed air. The conventional compressed-air breaking cylinder is fundamentally a bevel end hollow cylinder with breaking-air slots or apertures on the circumference, to which a high pressure compressed air duct is joined by the intermediary of a crack disk. At the present time in coal mining, the conventional single cylinder breaking unit is fed from an air duct with a maximum pressure of 100 MN/m.sup.2. In the case of such units the breaking length or depth is 1-2 m per operation in plain coal deposits and a maximum 6 m in steep dip coal deposits. In plain coal beds the breaking depth is increased by a multistep slow operation with consecutive breaking sections of 1-1.5 m length, while in steep dip coal beds, applying tearing down of top coal without support, this is impossible, because the top wall over the broken area tears away in mose cases. When the breaking holes are bored longer than as stated above, and in the bottom of a hole a single cylinder breaking unit is actuated, then a loosening and/or breaking effect will not be attained in spite of the operation of the cylinder and only a compaction will be brought about. For applying an explosive procedure, the periodical evacuation of the air passage is obligatory.
The disadvantages of present methods are the small breaking length, low productivity, and the fact that for loosening and/or breaking steep dip, gaseous deposits when applying tearing down of top coal without support, these methods have only low productivity and, on account of tearing away of the top wall, also result in high losses of coal resources.
Moreover, the conventional breaking cylinders with a crack disk have the disadvantage in that the coal is broken by the air over the total circumference of the cylinder and so with low efficiency.